A Methodology of Assessing Nonpoint Source Pollution from Agricultural Watersheds

Appraisals of water quality impacts induced by applying watershed management practices are difficult due to many factors. Lack of existing research data base, the diffusive characteristics of nonpoint source pollutants, and the technical difficulties to relate the instream water quality to the topographic features, soil characteristics, land use, land cover, soil moisture conditions, and the management practices in the watersheds. In order to overcome these difficulties, two field projects have been developed to investigate the impacts of watershed management practices in Illinois. The methods used in these two projects are presented. The basic techniques may be divided into three categories: field monitoring, geographical information system, and watershed modeling. These three components are mutually dependent.